Think twice before snacking on chips while preaching at your toddler to eat his broccoli: new research finds that habits ingrained in childhood may persist in adulthood, even withstanding later social influences, to affect body weight.

Researchers at Newcastle University in England looked at brother and sister pairs to assess how their upbringing and experiences affected their body-mass index (BMI), a measurement that gauges body fat. Relying on data from a University of Michigan study, they studied 236 sibling pairs aged 10 to 18 who were living together, and 840 adult sibling pairs living apart.

The researchers looked at various factors that could be responsible for similarities in the siblings’ BMI — things like whether they ate breakfast daily or participated in after-school sports. Common genes and upbringing are of course responsible for some of the obesity between siblings, but the researchers homed in on what they called “modifiable factors” — environmental or social influences like friends, access to parks and bike paths, or proximity to supermarkets that sell healthy food — to see if the same changeable factors associated with BMI in younger siblings also held up in adult brothers and sisters who lived separately.

The authors found that between the ages of 10 and 18, siblings exhibited similar patterns in exercise and eating, which influenced their BMI. If they ate healthy foods and exercised regularly, their BMIs were lower; the converse was true as well. When they applied the same analysis to adult sibling pairs aged 27 to 55, they found similar patterns.

But, interestingly, modifiable environmental factors held sway only in childhood. Although factors like living near a park or having fit friends influenced weight in the younger siblings, that effect disappeared in adulthood. Once siblings were living apart, it seemed that it was the constant, unchangeable factors like shared genes and upbringing that more strongly influenced their BMI. “Your shared childhood experience is important,” says Heather Brown, lead author and a lecturer in health economics at Newcastle University, but “your environment does not have lasting effects.”

The researchers say their findings upend the popular belief that social networks and environment heavily determine our personal norms about healthy weight. The upshot is this: habits formed in childhood related to eating and exercise carry over in adulthood, long after you’ve left home.

The conclusions shore up efforts to combat childhood obesity as a means of preventing weight problems later in life. Obesity rates continue to climb in the U.S.: between 1990 and 2007, they increased 13%. In Mississippi, our fattest state, 34% of adults are considered obese. “This demonstrates the importance of early childhood interventions and prevention programs to promote a healthier population,” write the authors in the journal Obesity.

For parents, Brown says the message is to be a culinary role model. If you choose healthy foods and moderate portions, your children will take note. Moreover, it’s important to start early. When researchers looked at 10-year-olds, their behavior had already stabilized, suggesting they learn eating norms in early childhood.

“If we don’t form good habits in childhood, obesity will continue to increase over time,” Brown says.

Bonnie Rochman is a reporter at TIME. Find her on Twitter at @brochman. You can also continue the discussion on TIME‘s Facebook page and on Twitter at @TIME.